This invention relates to an electronic communication device shelf unit for mounting or packaging printed circuit boards thereto or therein, and also to an assembly composed of the shelf units put one on another.
Generally, shelf units for mounting printed circuit boards thereto are put one upon another and arranged side by side in a matrix arrangement, for example in a cabinet, to give a beautiful appearance or to protect from foreign substances, such as dust, and to provide a framed device. Electronic components provided on a printed circuit board (which will be referred to as a PC board hereinafter) generate heat, and as a result a collection of PC boards generate a large amount of heat. It is, therefore, very important to effectively radiate or diffuse this large amount of heat out of the frame device.
For the purpose of radiating of heat from the frame device in a conventional frame device, a heat diffusing inclined plate is provided on the top of each of the shelf units. Hot air from the shelf units flows upwards in the shelf units to the inclined plates and then flows along the inclined plates so that the hot air is introduced into spaces between the shelf units and the cabinet. The hot air in the spaces which are connected to a common vertical extending chimney passage is collected in an upper space of the cabinet, due to the so-called chimney effect. The hot air collected in the upper space of the cabinet is finally discharged out of the cabinet through a number of outlet windows or openings provided on an upper plate of the cabinet.
However, this means of radiating of hot air according to the prior art, wherein the hot air from all the shelf units is collected at one place, i.e. at the upper space of the cabinet, tends to free the upper space with hot air, which thus results in a great difference in temperature between the top and the bottom of the cabinet. It should be noted that the allowable maximum value of the amount of generated heat for the whole frame device depends on the temperature of the hot air in the upper space of the cabinet, because the temperature in the upper space of the cabinet is highest. Therefore, an allowable maximum value of the amount of generated heat for a PC board is limited to a lower value, which thus results in an undersirable limitation on the PC board. This limitation means a decrease in the packaging density of the electric components on the PC board.
Furthermore, in the prior art arrangement, although a number of outlet windows or openings are provided not only on the top cover of the cabinet, but also on side plates of the cabinet, almost all of the hot air can be radiated only through the outlet windows on the top cover, since the hot air having a high temperature flows in an upward direction in the cabinet. Therefore, ineffective heat radiation can be expected from the prior art arrangement, which is one of the reasons that the hot air tends to remain in the cabinet.